This invention is related to commonly owned U.S. Pat. No. 4,631,603 entitled xe2x80x9cMETHOD AND APPARATUS FOR PROCESSING A VIDEO SIGNAL SO AS TO BE ABLE TO PROHIBIT THE MAKING OF ACCEPTABLE VIDEO TAPE RECORDINGS THEREOFxe2x80x9d which issued on Dec. 12, 1986; to U.S. Pat. No. 4,695,901 entitled xe2x80x9cMETHOD AND APPARATUS FOR REMOVING PSEUDO-SYNC PULSES AND/OR AGC PULSES FROM A VIDEO SIGNALxe2x80x9d which issued on Sep. 22, 1987; to U.S. Pat. No. 4,907,093 for METHOD AND APPARATUS FOR PREVENTING THE COPYING OF A VIDEO PROGRAMxe2x80x9d which issued Mar. 6, 1990; to U.S. Pat. No. 4,819,098 for xe2x80x9cMETHOD AND APPARATUS FOR CLUSTERING MODIFICATIONS MADE TO A VIDEO SIGNAL TO INHIBIT THE MAKING OF ACCEPTABLE VIDEO TAPE RECORDINGSxe2x80x9d which issued on Apr. 4, 1989; to U.S. Pat. No. 5,157,510 for xe2x80x9cMETHOD AND APPARATUS FOR DISABLING ANTICOPY PROTECTION SYSTEM IN VIDEO SIGNALS USING PULSE NARROWING which issued on Oct. 20, 1992; to U.S. Pat. No. 5,194,965 for xe2x80x9cMETHOD AND APPARATUS FOR DISABLING ANTI-COPY PROTECTION SYSTEM IN VIDEO SIGNALSxe2x80x9d issued on Mar. 16, 1993; to U.S. Pat. No. 5,625,691 for xe2x80x9cMETHOD AND APPARATUS TO DEFEAT CERTAIN COPY PROTECTION PULSES WITHIN A VIDEO SIGNALxe2x80x9d issued on Apr. 29, 1997; to U.S. Pat. No. 5,633,927 for VIDEO COPY PROTECTION PROCESS ENHANCEMENT TO INTRODUCE HORIZONTAL AND VERTICAL PICTURE DISTORTIONSxe2x80x9d issued on May 27, 1997; to U.S. Pat. No. 5,748,733 for xe2x80x9cMETHOD AND APPARATUS TO REDUCE EFFECTS OF CERTAIN COPY PROTECTION PULSES WITHIN A VIDEO SIGNALxe2x80x9d issued on May 5, 1998; to U.S. Pat. No. 5,661,801 for xe2x80x9cMETHOD AND APPARATUS FOR STABILIZING AND BRIGHTENING PRERECORDED TV SIGNALS ENCODED WITH COPY PROTECTIONxe2x80x9d issued on Aug. 26, 1997; to U.S. Pat. No. 4,336,554 for xe2x80x9cCODE SIGNAL BLANKING APPARATUSxe2x80x9d issued on Jun. 22, 1982 and to U.S. Pat. No. 5,583,936 for xe2x80x9cVIDEO COPY PROTECTION PROCESS ENHANCEMENT TO INTRODUCE HORIZONTAL AND VERTICAL PICTURE DISTORTIONSxe2x80x9d issued on Dec. 10, 1996. All of the above are incorporated by reference.
Also related is U.S. Pat. No. 4,163,253 for xe2x80x9cMETHOD APPARATUS FOR MODIFYING A VIDEO SIGNAL TO PREVENT UNAUTHORIZED RECORDING AND REPRODUCTION THEREOFxe2x80x9d issued on Jul. 31, 1979.
1. Field of the Invention
The field of the invention is in the mechanisms and/or methods for defeating, removing, or reducing the effects of the video copy protection signals. These mechanisms are also used to synthesize and improve the performance of a video copy protection signal.
2. Description of the Prior Art
The Hollywood movie industry is very concerned about the unauthorized copying of movies and programs. As an example, on Sep. 17, 1997 Jack Valenti, President and Chief Executive Office of the Motion Picture Association of America stated xe2x80x9cIf you can""t protect what you ownxe2x80x94You don""t own anything.xe2x80x9d The patent by Ryan, U.S. Pat. No. 4,631,603, incorporated by reference, discloses a way to process an ordinary program video source to have copy protection. The copy protected video is viewable on a TV set but it produces a recording lacking any entertainment value. That is, the video programs that are not recordable suffer from artifacts ranging from low contrast to synchronizing problems. The ""603 patent describes a method for xe2x80x9cconfusingxe2x80x9d or causing misoperation of the AGC system in a videocassette recorder while not causing a black depression problem in a television receiver displaying the copy protected signal.
A Polish Patent Application (PL 304477 (""477)) by Tomasz Urbaniec entitled xe2x80x9cMethod and Device for Protecting Videophonic Recordings Against Authorized Copyingxe2x80x9d filed Jul. 28, 1994, hereby incorporated by reference, discloses a variation of the ""603 patent by Ryan. FIG. 1a of the ""603 patent describes the waveform of the copy protected video signal as disclosed by Ryan and is replicated herein as FIG. 1a. FIG. 4 of the Urbaniec patent ""477 describes the comparative waveform as disclosed by Urbaniec, which is replicated herein as FIG. 1(b).
As is well known in the art, the videocassette system has a limited luminance frequency response, less than 2 MHz. A signal as described by Ryan recorded on a videocassette duplicating recorder with the AGC turned off (to avoid the effects of copy protection) will produce a video signal with pulse shapes modified by the limited frequency response of the duplicating recorder. Since there is no gap between the pseudo sync pulses and the AGC pulses of Ryan, the AGC system of a home duplicating recorder will respond to the combination of the pseudo sync pulses and the AGC pulses.
The limited bandwidth of the recording VCR responds slightly differently to the combination of pseudo-sync and AGC pulses separated by a time gap of 0.5 xcexcseconds to 2.0 xcexcseconds. If the time gap is as low as 0.5 xcexcseconds, the limited bandwidth of the recording videocassette recorder distorts the time gap to effectively remove it and the effectiveness of the copy protection is essentially the same as that achieved by Ryan. As the gap widens, the effectiveness of the copy protection is reduced or removed.
To defeat the copy protection process, there are a number of known ways such as attenuating, blanking, narrowing, level shifting, modifying and/or clipping the copy protection pulses as described in U.S. Pat. Nos. 4,695,901 (""901), 4,336,554 (""554), 5,157,510 (""510), 5,194,965 (""965), 5,583,936 (""936), 5,633,927 (""927), 5,748,733 (""733) and 5,661,801 (""801) cited above and hereby incorporated by reference.
In the patents mentioned above, the AGC and/or sync or pseudo sync pulses (see U.S. Pat. No. 4,695,901) are changed in amplitude, changed in level relative to normal sync pulses, and/or changed in pulse width, so as to allow a satisfactory recording.
In particular, U.S. Pat. Nos. 5,194,965 and 5,157,510 disclose narrowing of the AGC and/or pseudo sync pulses so that the record VCR does not sense these narrowed added pulses and thus, makes a satisfactory copy.
To defeat the anti-copy signal, the present invention discloses a method and apparatus utilizing pulse position and pulse width modulation of the AGC and/or sync or pseudo sync pulses. The invention also discloses the insertion of a sufficiently wide time gap between the AGC and/or pseudo sync pulses such that the record VCR will respond to or sense the sync or pseudo sync pulses but still will allow for a recordable copy.
The copy protection defeating mechanisms of this invention can also be used in combination with any of the defeat inventions mentioned above. For example, to defeat the copy protection process, one can shift (delay) the AGC pulse by about 1.5 xcexcseconds away from the preceding pseudo sync pulse and then trim the trailing edge of the preceding pseudo sync pulse by 0.6 xcexcsecond. Thus a gap of about 2.1 xcexcseconds exists between the trailing edge of the trimmed pseudo sync pulse and the leading edge of the delayed AGC pulse. If this gap is, for example, near blanking level for 2.1 xcexcseconds, then the VCR will sample the voltage in the gap instead of the added AGC pulses for its AGC amplifier. By sampling this gap voltage near blanking level, the copy protection signal is then nullified. Alternatively, the gap voltage level may be set above or below blanking level. It is important to note that by simply delaying or shifting the position of the leading edge of the AGC pulse relative to the trailing edge of the pseudo sync pulse, the gap between the pseudo sync pulses and the AGC pulses will nullify or partially nullify the effects of the AGC copy protection signal. It is also possible to create this gap in other ways such as moving the trailing edge of pseudo sync pulse away from the leading edge of the upcoming AGC pulse, or some combination of moving the position of both the AGC pulse and pseudo sync pulse to form a gap that would defeat the copy protection process. Typical gap durations of 1.5 xcexcseconds or more have proved effective in defeating the copy protection signal. Compounding the narrowing of the pseudo sync pulses and/or AGC pulses with this gap further enhances defeating the copy protection signal.
It should be noted that the defeat method as described above can be varied and then used as a copy protection signal. By dynamically varying the gap from zero to greater than 1.5 xcexcseconds between the trailing edge of the pseudo sync pulse relative to the leading edge of the upcoming AGC pulse, a new copy protection signal is made to effectively mimic the Ryan ""603 patent with amplitude modulated AGC pulses. By varying the gap via position modulation of the pseudo sync pulses relative to the AGC pulse or vice versa, or dynamically narrowing or changing the pulse width of the added pulses (AGC pulse and/or sync or pseudo sync pulse), an easier copy protection implementation is possible in the digital domain and/or analog domain. Today""s digital domain is the format of choice for implementing copy protection in cable systems and the like (i.e. digital versatile disc players). The range of pulse widths can be for example, between about 50% to 100% of the normal pulse widths (i.e. the pseudo sync pulse normal widths are about 2.3 xcexcseconds and the AGC normal widths are about 2.3 xcexcseconds to 3 xcexcseconds depending on how many added pulses are in a television (TV) line).
In general the copy protection process of the invention may start having the added pulse pairs as for example in FIG. 2(a) of Ryan ""603 patent, where the AGC pulse and/or pseudo sync pulse are position separated relative to time. If the gap due to position separation is insufficient to xe2x80x9cturn offxe2x80x9d the copy protection process (i.e. position modulation amounts to only 1.0 xcexcsecond of gap), then the AGC pulse and/or pseudo sync pulse can be narrowed as a function of time to increase the gap sufficiently (i.e. slowly trim or narrow the AGC pulse and/or pseudo sync pulse by about 0.35 xcexcsecond each, which would add another 0.7 xcexcsecond to the 1.0 xcexcsecond gap for a increased gap duration of 1.7 xcexcseconds). After the gap has been extended as to xe2x80x9cdefeatxe2x80x9d or turn off the copy protection signal, then the new copy protection signal is reactivated by reducing the separation (for example, to zero) between the AGC pulse and pseudo sync pulse and by restoring the pulse widths of the (trimmed or narrowed) AGC pulses and/or pseudo sync pulse to their full normal pulse widths.
The method of using relative position modulation between the sync and AGC pulses for defeating and/or synthesizing a copy protection signal can be applied to the copy protection pulses within or around a horizontal blanking interval. The method can also be combined with narrowing any portion of the added pulses.
In order to produce a further effective copy protection signal, a variation of the U.S. Pat. No. 4,631,603 patent has been developed. To this end, the AGC pulses also are amplitude modulated from full amplitude to zero and vice versa over the period of for example about 20 to 30 seconds. As a result, the illegal copy will have constantly changing brightness levels. This causes more annoyance when compared to a constant dim picture (when the AGC pulses are static and at full amplitude).